This section provides background information related to the present disclosure which is not necessarily prior art.
Underground utility lines are sometimes installed using any of a variety of trenchless installation technologies, including horizontal boring technologies. Horizontal boring technologies provide efficient and cost effective ways to install gas, water, electric and communications lines, particularly when it is difficult or cost prohibitive to plow or trench the ground, such as when there are ground obstructions (e.g., a road, sidewalk, driveway, or landscaping) along the path of the utility line that prevent those techniques. Some horizontal boring technologies include underground pneumatic boring, auger boring, wet boring, horizontal directional drilling (HDD), impact moling, pipe jacking and microtunneling.
The process of underground pneumatic boring involves launching a pneumatic boring or piercing tool that creates a horizontal bore hole along a straight path to create a tunnel through the ground. A utility line (e.g., for gas, water, electric or communications) can then be pulled back through the tunnel for installation underground.
A conventional system and method for underground pneumatic boring can be understood with reference to FIGS. 1A, 1B and 1C. In an area 10 where a new underground utility line is to be installed, the existing utility lines and a surface obstacle 12 (e.g., a road) to be traversed by the new utility line is surveyed. Then a path along which to create an underground bore or tunnel 14 for the new utility line is chosen. Thereafter, two pits are excavated on the opposite sides of the obstacle; a pit 16 at the path's origin (the entrance pit) and a pit 18 at its target destination (the exit pit). The pits 16, 18 are large enough to fit a boring tool 20 and to permit an operator to work. The pits are also deep enough so that as the boring tool 20 creates the tunnel 14, the surface of the ground above it remains undisturbed.
The boring tool 20, shown best in FIG. 1C, is a well-known device and comprises a pneumatically-operated boring tool that cuts through soil, rock, etc. The boring tool 20 is connected to a supply of compressed air by an air supply hose 22. A guide tool 24 and a sighting device 26 (both shown in FIG. 1B) are used to align the boring tool along the desired path and toward the intended destination. The boring tool 20 is then activated and it proceeds to cut the tunnel 14, advancing through the wall of the entrance pit with the air supply hose 22 following behind it. Once the boring tool 20 has progressed beyond the guide tool 24, the location of the boring tool 20 is tracked through the ground with a radio frequency receiver that detects a radio signal generated by a radio transmitter that is built into the boring tool.
When the boring tool 20 reaches the target destination, it has completed the tunnel 14 through which the new utility line can be run, between the entrance and exit pits 16, 18 and beneath the surface obstacle 12. The boring tool 20 is then removed from the air supply hose 22. The utility line is then attached to the air supply hose 22 (such as by taping the utility line to the hose 22), and the hose 22 and utility line are pulled back through the tunnel together, thereby installing the utility line underground.
Underground pneumatic boring, however, has drawbacks which can result in difficulties in completing a bore for an underground utility line. For example, the boring tool is not steerable, and once it has exited the guide tool the operator no longer has control over the boring tool's trajectory. Consequently, the boring tool can be deflected from the desired path by rocks and different soil densities, for example. Even minor deflections can cause significant deviations from the desired path over long distances. Consequently, the boring tool could unintentionally cross the path of other already existing underground utilities. Therefore, and notwithstanding the fact that existing underground utility lines are located and marked from above ground before the pneumatic boring underground is carried out, it is possible that the boring tool can tunnel through an existing utility line, such as a sanitary sewer line, without the operator knowing. Then, when the new utility line is installed it would run right through the existing sewer line. In such an instance, a crossbore—that is, an intersection of two or more underground utilities—is created.
A significant concern for the underground utility construction industry, regardless of the horizontal boring process employed, is unknowingly tunneling through a sewer line and thereafter running a utility line, such as a natural gas pipeline or power line, through the sewer line. The crossbored utility line may remain in place for months or years before a blockage develops in the sewer line. Then, in the process of clearing the sewer line, the utility line can be severed, ruptured, or otherwise damaged by a power drain auger or other tool or machine that is used to clear the sewer line. Any resulting damage to the crossbored utility line can lead to a catastrophic failure, such as an explosion, if the crossbored utility line is a gas line; or injury to the operator of the sewer cleaning machine if the crossbored utility line is a power line; or disruption of services if the crossbored utility line is a communications line, for example.